Socially and professionally, most people rely upon video displays in one form or another for at least a portion of their work and/or recreation. With a growing demand for large screens, such as high definition television (HDTV), cathode ray tubes (CRTs) have largely given way to displays composed of liquid crystal devices (LCDs), plasma display panels (PDPs) or front or rear projection systems.
A CRT operates by scanning electron beam(s) that excite phosphor materials on the back side of a transparent screen, wherein the intensity of each pixel is commonly tied to the intensity of the electron beam. With a PDP, each pixel is an individual light-emitting device capable of generating its own light. With an LCD, each pixel is a back-lit, light modulating liquid crystal device.
As neither system utilizes a large tube, LCD and PDP screens may be quite thin and often are lighter than comparable CRT displays. However, the manufacturing process for LCDs, PDPs, and most other flat panel displays is much more complex and intensive with respect to both equipment and materials than that of CRTs, typically resulting in higher selling prices.
Projection systems offer alternatives to PDP and LCD based systems. In many cases, projection display systems are less expensive than comparably sized PDP or LCD display systems. Rear projection display systems typically employ a wide angle projection lens (or multiple lenses), operating in connection with one or more reflective surfaces to direct light received from the projector through the lens(es) to the back of a screen. The lens and mirror arrangement typically enlarges the image as well.
To accommodate the projector, one or more lenses, and reflectors, rear projection displays are typically 18 to 20 inches deep and not suitable for on-wall mounting. A typical rear projection system offering a 55-inch HDTV screen may weigh less than a comparable CRT, but at 200+ pounds it may still be difficult and awkward to install and support.
Often, rear projection display devices exhibit average or below average picture quality in certain environments. For example, rear projection displays may be difficult to see when viewed from particular angles within a room setting or when light varies within the environment. Aside from a theatrical setting, light output and contrast is a constant issue in most settings and viewing environments.
Despite advancements in projectors and enhanced lens elements, the lens and reflector design remains generally unchanged and tends to be a limiting factor in both picture quality and overall display system thickness.
A developing variation of rear projection displays utilizes light guides, such as optical fibers, to route an image from an input location to an output location and to magnify the image. Such displays may be referred to as light guide screens (LGSs). However, in certain configurations, light guide screens may lose a percentage of light and, thus, the brightness of the image.
In many cases, the light guide elements occupy a fraction of the area of the input surface and significant fraction of the input surface is occupied with clad or filler material. Thus only a fraction of the light from the projection source is coupled into the lightguide, causing a loss of image brightness.
Weight, thickness, durability, cost, aesthetic appearance and quality are key considerations for rear projection display systems and display screens. From the manufacturing point of view, cost of production and increased yield are also important.
Hence, there is a need for a rear projection display that overcomes one or more of the drawbacks identified above.